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  <title>Document</title>
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<body>

  <script>
    const arr = [
      { 'id': '29', 'pid': '', 'name': '总裁办' },
      { 'id': '2c', 'pid': '', 'name': '财务部' },
      { 'id': '2d', 'pid': '2c', 'name': '财务核算部' },
      { 'id': '2f', 'pid': '2c', 'name': '薪资管理部' },
      { 'id': 'd2', 'pid': '', 'name': '技术部' },
      { 'id': 'd3', 'pid': 'd2', 'name': 'Java研发部' },
      { 'id': '2g', 'pid': 'd2', 'name': 'Python研发部' },
    ]

    function transDataTree(arr) {
      const mapObj = {}
      arr.forEach(item => {
        if (!item.children) {
          item.children = []
        }
        mapObj[item.id] = item
      })
      console.log(mapObj)

      const newArr = []
      arr.forEach(item => {
        const parent = mapObj[item.pid]
        if (parent) {
          parent.children.push(item)
        } else {
          newArr.push(item)
        }
      })
      return newArr
    }
    transDataTree(arr)
  </script>
</body>

</html>